This application claims priority to Canadian Patent Application No. 2,296,964, filed on Jan. 25, 2000 the complete disclosure of which is incorporated herein by reference.
This invention relates to a method and apparatus for the recovery of cobalt from impure cobalt, particularly from cobalt containing minerals, ores, scrap, slag, concentrates, metallurgical intermediates and by-products and, more particularly, nickel-and iron-containing materials.
It is well-known that metals such as, for example, nickel and iron can be recovered from reduced metal-containing mixtures, using carbonylation processes. Volatile nickel and iron carbonyls are formed at elevated temperatures and pressures, separated, isolated and thermally decomposed to yield pure metal pellets and carbon monoxide gas. The purity of the nickel metal produced by this process is extremely high because of the selectivity of the carbonylation reaction and the fact that other metals, often present with nickel, are either easily separated, or do not form gaseous compounds. However, in contrast, iron carbonyl cannot be completely separated from nickel carbonyl because these compounds form an inseparable isotropic mixture.
It has been reported that cobalt, which is often present with nickel and iron in metal-containing mixtures, such as ores and tailings, together forms a cobalt carbonyl under similar conditions particularly, when hydrogen is used, together with carbon monoxide for the formation of carbonyls. Cobalt carbonyl, having much lower vapour pressure than nickel and iron carbonyls, usually remains in the carbonyl reactor together with solid leftovers of the carbonylation reaction, or is partially carried, together with volatile carbonyls, and left as a solid residue after nickel and iron carbonyls"" fractional separation. The further isolation of cobalt usually involves desolution of cobalt in acid, followed by electrowinning.
Similarly, carbonylation of metals-containing mixture as in alkaline solution leads to the formation of gaseous nickel carbonyl as well as iron and cobalt carbonyl compounds that remain the solution. A further refining of cobalt involves an acidification of the solution, followed by cobalt organic solvent extraction. The extracted cobalt is then purified by electrowinning.
There have been several attempts to achieve cobalt extraction using volatile cobalt carbonyl precursors such as cobalt hydrocarbonyl. For example, when a slurry of cobalt, nickel and copper metals were treated with a carbon monoxide-hydrogen gas mixture at 68 bar pressure, mixtures of nickel carbonyl and cobalt carbonyl anions were produced. Volatile nickel carbonyl was degassed from the solution and the residue was filtered out. The basic solution of cobalt carbonyl salt was acidified with strong acid and volatile cobalt hydrocarbonyl boiled and removed from solution. Subsequent decomposition of cobalt hydrocarbonyl resulted in a pure cobalt metal containing 30 ppm of Ni, 0.4 ppm of Fe and 0.1 ppm of copper. This procedure involves several handling processes, including filtration of the solution, dilution and acidification of the resulting solution.
Other separations of cobalt carbonyl from nickel carbonyl involved addition of ammonia to precipitate {Co(NH3)6][Co(CO)4]2, or cobalt removal by passage through ethanolic KOH.
It is known that iron nitrosyl carbonyl Fe(NO)2(CO)2 has been prepared in the gaseous state by the reaction of NO with FE(CO)5 at 95xc2x0 C., and in aqueous alkaline solution. However, I have discovered that CoNO(CO)3 can be beneficiously and efficaciously distilled from Fe-containing carbonyl species to provide Fe-free CoNO(CO)3 gas for subsequent decomposition to pure cobalt metal (99.8%).
It is an object of the present invention to provide apparatus and process for producing purified cobalt from mixtures comprising impure metallic cobalt or compounds thereof, in admixture with metallic nickel and/or iron or compounds thereof.
In its broadest aspect, the invention provides a process for producing purified cobalt from a mixture comprising metallic species of cobalt and metallic species of at least one of the group consisting of nickel and iron; said process comprising
producing a metal carbonyl mixture of cobalt carbonyl and at least one of said nickel carbonyl and iron carbonyl from said metallic species mixture;
separating said nickel carbonyl and/or iron carbonyl from said cobalt carbonyl to provide a nickel carbonyl- and iron carbonyl-free resultant mixture;
treating said resultant mixture with an effective amount of a complexing gaseous mixture of nitric oxide/carbon monoxide to produce cobalt nitrosyl tricarbonyl;
decomposing said cobalt nitrosyl carbonyl to provide said purified cobalt and regenerated complexing gaseous mixture; and
removing said regenerated complexing gaseous mixture.
In one preferred aspect the invention provides a process for producing purified cobalt from a mixture comprising metallic species of cobalt, and at least one of the group consisting of nickel and iron; said process comprising
(i) reacting said metallic species with carbon monoxide to form a carbonyl mixture comprising cobalt carbonyl and nickel carbonyl and/or iron carbonyl, provided that when said metallic species comprises non-elemental metal species, said mixture is, optionally, first treated with a reducing agent to reduce said non-elemental metallic species to said elemental metal;
(ii) removing said nickel carbonyl and said iron carbonyl by distillation from said carbonyl mixture to provide a nickel- and iron-depleted impure cobalt carbonyl mixture;
(iii) treating said impure cobalt carbonyl mixture with an effective amount of a complexing gaseous mixture of nitric oxide/carbon monoxide to produce cobalt nitrosyl carbonyl;
(iv) decomposing said cobalt nitrosyl carbonyl to provide said purified cobalt and regenerated complexing gaseous mixture; and
(v) removing said regenerated complexing gaseous mixture.
By the term xe2x80x9cmetallic speciesxe2x80x9d in this specification is meant to include the metal in the form of the elemental metal per se, sulfides, oxides, salts thereof, and minerals, concentrates, metallurgical intermediates, by-products and the like containing said elemental metal, sulfide, oxide and salts; and mixtures thereof.
It will be readily understood by the. skilled person in the art that the process as hereinabove defined does not require the optional reduction step when the mixture does not contain sufficient reducable non-elemental metal compounds as hereinabove defined. The optional reduction step may be carried out by reducing agents, such as for example, carbon monoxide, hydrogen or mixtures thereof. The aforesaid carbonylation step (i) may be carried out simultaneously as the optional carbon monoxide reduction to elemental metal step.
Surprisingly, I have discovered that to effectively separate cobalt from nickel-and/or iron containing admixtures according to one aspect of the present invention, that both nickel carbonyl and/or iron carbonyl must be removed first from the cobalt carbonyl containing admixture, in the complexing reaction vessel. Subsequent production and isolation of complexed cobalt carbonyl compounds, such as for example, cobalt nitrosyl tricarbonyl provides a desired pyrolysable precursor for purified metal cobalt production.
By the term xe2x80x9cnickel carbonyl- and iron carbonyl-freexe2x80x9d is meant in this specification and claims that the amount of these metal carbonyls may be extremely low, but not necessarily absolute. The amount that can be tolerated in the practice of the invention is that which does not result in greater than 0.1% w/w of each of nickel and iron as metal in the resultant purified cobalt product. An important aspect of the present invention is that although iron nitrosyl carbonyl has been reported to exist, it either is not formed or does not vaporize in addition with the cobalt nitrosyl tricarbonyl and carried over to the vapour deposition reactor for co-deposition with the cobalt.
Most preferably, the nickel carbonyl and/or iron carbonyl gases of step (ii) are subsequently pyrolysed to provide regenerated carbon monoxide for recycle to step (i). Yet further, preferably, the regenerated complexing gaseous mixture of step (vi) is recycled to step (iii).
Thus, recycling of aforesaid gaseous carbon monoxide advantageously provides for a continuous, closed-loop, purified cobalt production process, preferably under the control of a computer algorithmic microprocessor means.
Accordingly, in a preferred aspect the invention provides a process as hereinbefore defined further comprising continuously self-monitoring, under the control of computer algorithmic microprocessor means, by measuring, controlling and adjusting process parameters selected from the group consisting of temperature, pressure, gaseous input flow rates, gaseous output flow rates and power supply.
The nickel carbonyl Ni(CO)4, and/or iron carbonyl Fe(CO)5 may be readily removed by vaporization, distillationxe2x80x94vacuum or otherwise, from the carbonylation reactor to leave behind cobalt carbonyl, (Co)2(CO)8.
In a further aspect the invention provides apparatus for producing purified cobalt from a mixture comprising metallic species of cobalt and metallic species of at least one of the group consisting of nickel and iron, said apparatus comprising
(i) means for producing a metal carbonyl mixture of cobalt carbonyl and at least one of said nickel carbonyl and iron carbonyl from said metallic species mixture;
(ii) vaporization means for separating said nickel carbonyl and said iron carbonyl from said cobalt carbonyl to provide a resultant nickel carbonyl-and iron carbonyl- free mixture;
(iii) means for treating said resultant mixture with an effective amount of a complexing gaseous mixture of nitric oxide/carbon monoxide to produce cobalt nitrosyl tricarbonyl;
(iv) means for decomposing said cobalt nitrosyl tricarbonyl to provide said purified cobalt and regenerated complexing gaseous mixture;
(v) means for recycling said regenerated complexing gaseous mixture to said means (iii) and
(vi) continuously self-monitoring computer algorithmic microprocessor means for measuring, controlling and adjusting process parameters selected from the group consisting of temperature, pressure, gaseous input flow rates, gaseous output flow rates, metal carbonyl, carbon monoxide, nitric oxide and cobalt nitrosyl tricarbonyl concentrations in gaseous state and power supply.
In an alternative preferred aspect, the invention provides a process for producing purified cobalt from a mixture comprising metallic species of cobalt and metallic species of at least one of the group consisting of nickel and iron; said process comprising
(i) treating said mixture in aqueous alkaline medium with hydrogen sulfide to effect reduction of metal species to soluble metallic species;
(ii) subsequently treating said medium with carbon monoxide to produce cobalt carbonyl in admixture with nickel carbonyl and/or iron carbonyl in aqueous slurry;
(iii) removing said nickel carbonyl, if any, by volatilization from said solution; to provide a nickel carbonyl-depleted slurry;
(iv) treating said cobalt carbonyl with an effective amount of a complexing gaseous mixture of nitric oxide/carbon monoxide mixture to produce cobalt nitrosyl tricarbonyl;
(v) isolating said complexed cobalt carbonyl by distillation to provide purified cobalt nitrosyl carbonyl;
(vi) decomposing said purified cobalt nitrosyl carbonyl to provide said purified cobalt and regenerated complexing gaseous mixture; and
(vii) removing said regenerated complexing gaseous mixture.